1. Field of the Invention
The present invention relates to a light source apparatus having a structure for controlling a temperature of a light source element.
2. Description of the Background Art
In recent years, in a light source apparatus such as a projector, an LED (Light Emitting Diode) element, a laser element (a semiconductor laser element) or the like is used in place of a conventional lamp light source based on a demand for increase in lifetime and power of a light source element. Each of the LED element and the laser element will be hereinafter referred to as a light source element.
The light source element has a characteristic that the output and the lifetime are reduced if a temperature is raised. Therefore, in order to maintain long lifetime and high power in the light source element, it is necessary to hold the temperature of the light source element to be low. A Peltier element, a cooling mechanism of a water cooling type or the like is utilized as means for cooling the light source element. The temperature of the light source element will be hereinafter referred to as an element temperature.
Moreover, in the case in which the element temperature of the light source element is varied, moreover, a wavelength of an optical output of the light source element is changed. In the case in which the light source element is applied to a so-called video apparatus such as a projector, a change in the wavelength of the light source element varies a hue. For this reason, it is necessary to cause the element temperature to be as constant as possible.
In a cooling apparatus including a freezing machine having, as cooling means, a so-called Peltier element, chiller, compressor or the like, there is a possibility that a temperature of a cooling surface of the light source element might be lower than a dew point temperature determined by an ambient environment. The ambient environment includes an ambient temperature, an ambient humidity and the like. Moreover, the dew point temperature indicates a temperature at which condensation is started. In this case, there is a fear that peripheral components including a light source element and an electric circuit system might break down due to water droplets generated by the condensation.
Therefore, Japanese Patent No. 3315461 (Paragraphs 0025 to 0029, FIG. 4) discloses the technique for taking measures against condensation which copes with a change in an ambient environment (which will be hereinafter referred to as the related art A). In the related art A, the environmental temperature and the environmental humidity are detected by means of the air sensor provided in the apparatus and the saturated vapor pressure is estimated therefrom. When the vapor pressure of the outside air exceeds the saturated vapor pressure, the control of the Peltier element is stopped to prevent the condensation.
However, the related art A has the following problem. In the related art A, the vapor pressure of the outside air exceeds the saturated vapor pressure in the timing for stopping the control of the Peltier element (the cooling mechanism). In the same timing, there is a possibility that the condensation might have occurred.
Moreover, in the related art A, the control of the Peltier element is stopped. For this reason, the element temperature of the light source element cannot be maintained to be constant due to the rise in the temperature after the stoppage. For this reason, there is a problem in that the hue is shifted due to the change in the wavelength. Furthermore, in the state in which the control of the Peltier element is stopped, the element temperature of the light source element is raised. For this reason, there is also a fear that a defect such as reduction in the lifetime of the element or the breakdown of the element might be caused. In other words, the related art A has a problem in that the element temperature cannot be maintained to be constant in order to prevent the defect.